The Investigation Of Photogenerated Electrons In TiO₂ Heterojunction Based Photocatalyst Via In-situ Irradiation X-ray Photoelectron Spectroscopy

The rapidly development of modern industry leads to serious problems such as over exploitation of energy and environmental pollution,which is also the primary environmental problem in the world.Hydrogen is not only a kind of clean energy with high calorific value but also no harm to environment.It is an effective way to replace traditional fossil energy with hydrogen to solve the environmental problems.However,the traditional method of hydrogen production consumes too much energy,which limits its application.The appearance of photocatalyst makes it possible to obtain hydrogen energy with low cost and barely no pollution,but its further application is limited due to its fast recombination rate of photogenerated electron-holes pairs.In order to limit the recombination of photogenerated electron hole pairs,it is an effective method to improve the separation efficiency by combining with other materials.At present,the most commonly used composite materials are semiconductor materials and noble metal or metal like conductor materials.However,the mechanism of improving the catalytic performance is only in the theoretical stage,and there are few experimental characterizations to verify this hypothesis,which will bring some obstacles to the future design of catalysts.The application of in-situ irradiation XPS technology makes it possible to capture this migration.Therefore,in this paper,titanium dioxide（TiO₂）was used as the main catalyst to study the photoelectron migration in the case of composite with semiconductors and metal like conductors.The catalytic performance and catalytic mechanism were further studied.Molybdenum disulfide（MoS₂）,as a narrow gap semiconductor material,is usually used as a cocatalyst to enhance photocatalytic activity.TiO₂nanofibers were prepared by electrospinning,and then MoS₂nanosheet were grown on the surface of TiO₂fibers by hydrothermal method.It was found that when the mass fraction of MoS₂reached 60%,the catalytic activity reached the maximum.In-situ irradiation XPS results show that the binding energy of Ti increases,while that of Mo decreases.According to the shielding effect,the photoelectron generated by UV excitation of TiO₂migrates to the surface of MoS₂through the interface between the two,which reduces the photoelectron recombination efficiency of TiO₂and improves the catalytic activity.Titanium carbide（Ti₃C₂）is a common material in MXene,which is widely used in energy storage and catalysis due to its metal like properties.Ti₃C₂with multilayer structure was prepared by chemical etching of Ti₃AlC₂,and then TiO₂nanoparticles were in-situ grown on the surface by hydrothermal method.It was found that the catalytic activity of Ti₃C₂was significantly higher than that of pure TiO₂.In-situ irradiation XPS results show that the binding energy of Ti-O in TiO₂increases,and that of Ti-C in Ti₃C₂decreases.This indicates that the photogenerated electron on TiO₂is transferred to Ti₃C₂through the interface between TiO₂and Ti₃C₂,which inhibits the recombination of photogenerated charge of TiO₂itself.By adjusting the hydrothermal time,it is found that the activity of the composite reaches the highest when the hydrothermal time is 8 hours,and the change of the binding energy in the in-situ irradiation XPS test also reaches the maximum.The results show that the ratio of TiO₂to Ti₃C₂can also affect the catalytic activity of the catalyst,which is not only reflected in the hydrogen production rate,but also in the in-situ irradiation XPS test.